num = input()

if len(num) < 4:
    print(0)
    exit(0)

len1 = [int(num[i]) for i in range(len(num))]
len2 = [int(num[i - 1] + num[i]) for i in range(1, len(num))]
len3 = [int(num[i - 2] + num[i - 1] + num[i]) for i in range(2, len(num))]
len4 = [int(num[i - 3] + num[i - 2] + num[i - 1]) for i in range(3, len(num))]

mx = 0 

for el in len1 + len2 + len3 + len4:
    prost = True
    
    for k in range(2, el):
        if el % k == 0:
            prost = False
    if prost:
        mx = max(mx, el)
        
        
print(mx)
